Photoreceptors convert received light rays into an analog electrical signal that can be digitalized. For example, photoreceptors can be situated in a digital camera that registers an arbitrary image in analog form, is digitalized following the photoreceptors and is further-processed in digitalized form, for example in a computer. However, the photoreceptors can also be utilized as an independent sensor system independently of a video camera, for example in image processing. A further employment of photoreceptors can be seen in a realization of what is referred to as a technical eye.
Various photoreceptor arrangements are known under the research term of silicone retina and are discussed in the following prior art references: K. Boahen and A. Andreou, A Contrast Sensitive Silicon Retina with Reciprocal Synapses, Advances in Neural Information Processing Systems 4, J. Moody et al. (eds.), San Mateo, pp. 764-772, (1992); J. Heeger et al., Image Enhancement with Polymer Grid Triode Arrays, Science, Vol. 270, pp. 1642-1644, (1995); M. Mahowald and C. Mead, The Silicon Retina, Scientific American, Vol. 164, pp. 40-46, (1991); S, Wolpert and E. Micheli-Tsanakou, Silicon Models of lateral Inhibition, IEEE Transactions on Neural Networks, Vol. 4, pp. 955-961, (1993); and Wu Chung-Yu and Chiu Chin-Fong, A New Structure of the 2-D Silicon Retina, IEEE Journal of Solid-State Circuits, Vol. 30, No. 8, pp. 890-897, (1995).
In the photoreceptor arrangements described therein, with which the retina of vertebrates is to be simulated, it is also known to embed the photoreceptors in a network. As a result of this procedure, it is beginning to become possible to implement a filtering of the registered image information. In said works, the coupling of the photoreceptors ensues mainly with the goal of intensifying contrast.
The known arrangements, however, exhibit some disadvantages and deliver only unsatisfactory results. In particular, the couplings in the cited networks are fixed and not fashioned variable dependent, for example, on the illumination intensity of the photoreceptor arrangement. These models can thus only be meaningfully employed in a small range of an illumination intensity predetermined by the coupling intensities.
The reference of J. Heeger et al., Image Enhancement with Polymer Grid Triode Arrays, Science, Vol. 270, pp. 1642-1644, (1995), also discloses that the photoreceptors be coupled to one another not by a network but via a substrate of fixed conductivity.
A Oppenheim and A. Willsky, Signale und Systeme, 2.sup.nd Edition, VCH Verlagsgesellschaft, ISBN 3-527-28433-8, pp. 347-383, (1992), discloses various filter structures of digital filters.
The German reference DE 43 37 160 A1, discloses a photodetector array. The photodetector array comprises a plurality of photodetector elements regularly arranged in a surface. At least two layers, layers A and B, are provided, whereby the photodetector elements are arranged in the first layer A facing toward the light incidence and are directly connected to one another via paths of controllable electrical conductivity, for example channels of MOS transistors. Further circuit elements are accommodated in a second layer arranged coplanar with the first.